—General Chuck Yeager (the first pilot to break the sound barrier) when asked how many UFOs he'd ever seen[1]

An Unidentified Flying Object or UFO (alternatively Unidentified Aerial Phenomenon, or UAP[2]) is any observed anomaly in the sky that is not identifiable as a known object or phenomenon. Alleged UFO sightings are associated with related crank claims, i.e. of visitation by intelligent extraterrestrial life or of government-related conspiracy theories.

Culturally, "Unidentified Flying Object" has come to mean "alien spacecraft" by default though sometimes the term ETV (ExtraTerrestrial Vehicle) is used to separate an alien vehicle from an unknown earth vehicle. A typical paradox is the fact that identifying UFOs as flying saucers negates the "U" part of UFO, of course, since if an object is said to be of alien origin, it can no longer be called "unidentified"...unless one is referring to which alien the craft belongs to.[note 1]

Alleged UFO sightings are more likely to occur at night, since many regular flying objects give off one or several peculiar lights, sometimes blinking, and sometimes seeming to disappear and re-appear due to clouds — which can be practically invisible at night.

The basic list of what needs to be eliminated before alien spacecraft is even worth considering includes known commercial and private air flights, to classified military flights, to experimental test flights of various planes and rockets (like those at Area 51), to rocket launches and corresponding spent-stage ejections, to weather balloons, to meteorites or space junk burning up in the atmosphere, to kites, to ball lightning, to atmospheric phenomena (like the Northern Lights,[3] or strangely lit clouds), to bright stars or planets (Venus is often reported as a UFO), to Iridium flares, to drones of various types, to pranksters, to video hoaxters (who fake their own evidence) and so on.

The first notable wave of interest in UFOs was actually in the 1890s. Interestingly, this helps put later waves of interest in UFOs in perspective: because popular culture had yet to define what a UFO was supposed to look like, the spacecraft described were rarely shaped like flying saucers (in one incident, the supposed craft was shaped "like a giant cigar") and the flashing lights later common to many stories were much rarer.[note 2] The craft were also much slower (though they would've seemed fast at the time).

"Foo fighter" was the term given by Allied pilots to unusual aerial phenomena and so-called UFOs they encountered during World War II. There were reports from both theatres of war, namely Europe and the Pacific. Various explanations have been put forward, including St. Elmo's Fire, Nazi secret weapons, ball lightning, the planet Venus, and even disoriented pilots suffering from vertigo.

On December 10, 1946, a U.S. Marine C-46 transport plane crashed on the southwest side of Mount Rainier in Washington State, and was not located until the next summer. [5] A private pilot named Kenneth Arnold volunteered to aid with the search. While he was circling the mountain he spotted a cluster of nine brightly glowing meteors rushing past his plane toward the massive, remote bulk of Mount Adams to the south.

Since they were pieces of a meteoric fireball in the process of breaking up, they seemed to be flying in formation, so Arnold assumed they were aircraft, and he naturally interpreted their brightness to be the Sun glinting off of polished aluminum. The pieces were tumbling, and this made them hop up and down in the airstream. Arnold told reporters they flew "like a saucer skipping over water."

This was a highly publicised UFO sighting, and it sparked a national obsession with "flying saucers" that bordered on mass hysteria. Suddenly there were many more sightings. Some were ordinary mistakes but most were outright copycat hoaxes. An important point that is often missed is how Arnold's description of the actions of his nine meteors skipping like saucers somehow got garbled into the shape of the objects being like saucers, and once that got locked into the public's mind, all UFOs suddenly began to look like saucers.

Many frauds came forward to push this hysteria, including George Adamski who claimed to have ridden across the Solar System with Venusians (unlikely, as the planet Venus is over 450°C[6]).

“”I know for a fact the first UFOs reported in modern times, just before the crash at Roswell, were boomerang-shaped and were reported as 'flying saucers' to describe the motion of their flight, like a saucer skipping over water. Yet immediately after, people saw and photographed saucer-shaped objects. Boomerang-shaped objects were rarely seen. Now people mostly report seeing large triangles instead of discs or boomerangs, because that is what they are told to expect to see.

—Thomm Quackenbush, Artificial Gods

In the late 1940s, the USAF ran Project Mogul, a top secret attempt to detect sound waves from potential Sovietnuclear explosions using microphones flown by high-altitude balloons. On July 7, 1947 Mogul Flight #4 crashed on a ranch near Roswell, New Mexico.[7][8] A rancher found the debris field and brought some of the debris to the nearby air base. The public information officer at Roswell Army Air Field made a press release reporting that a crashed "flying disc" has been recovered. The press went nuts, cementing the meme of the "flying saucer" in the public's consciousness. After the sensation hit the headlines, the officer was reprimanded, and new information was announced: the wreckage was from a weather balloon. Years after the fact, the story got embellished and mutated into different versions, becoming the archetypal "crashed saucer" myth, complete with recovered alien corpses (or live aliens!) and a government cover-up.

The "mother ship" from Close Encounters of the Third Kind, now housed at the Smithsonian

The first event was the assassination of President John F. Kennedy in 1963, which sparked a poisonous conspiracy mindset that, before, had largely been found only within fringe groups. The second, the Tet Offensive in 1968, seemed to validate this mindset to many people, who realized with shock that the government had lied to them and victory in the Vietnam War was actually nowhere in sight. The third and final event was the cover-ups and incredible abuses of power of the Nixon Administration in the Watergate affair.

It was only after this vast attitude shift occurred that people looked back and read ominous things into the comedy of errors that took place at the beginning of the UFO era. Alien bases were imagined to exist in the southwestern United States. An entire alphabet soup of imaginary government agencies were cooked up, which supposedly controlled all information on the alien presence. Even the information that these agencies existed was, conveniently, also classified as top secret. There were imaginary projects to recover downed flying saucers and imaginary projects to overhaul and test-fly recovered flying saucers. And the very lack of evidence for any of these claims was put forth as proof that a conspiracy to hide the truth existed.

In the Fall of 1977 and again in the Spring of 1982, Steven Spielberg made a pair of movies (Close Encounters of the Third Kind and E.T. the Extra-Terrestrial) with "good" aliens and "bad" federal agencies, which tapped into the new mythology and made enormous amounts of money. In reality, no coordinated government plan to respond to alien contact, if there even is/was any, has ever been made public. A side effect of Close Encounters was to generate a new idea of UFO appearance, informing the shapes and designs of what appeared in blurry photographs from 1977 onwards.

It has been alleged by at least one wing-nut[9] that the government created the alien conspiracy theories to provide a cover for other projects, such as the Lockheed Skunk Works. Gullible farmers would be shown so-called "alien crash sites," and told to keep quiet. This cunning plan did two things:

“”The UFOs were explicable enough, just experimental aircrafts from the airport. Of course the government was not going to tell people what was actually going on. She would not be surprised if the government encouraged the UFO cultists to flock there as the perfect cover, since no one would ever believe them.

The USAF did actually launch an investigation of UFOs — Project Blue Book — that lasted between 1952 and 1970. It didn't find anything interesting.[note 3] They received technical assistance from imagery interpretation specialists at the Central Intelligence Agency.

CIA documents indicate that the agency monitored the UFO situation from 1952.[11]
In 1952, the CIA reacted to the new rash of sightings by forming a special study group within the Office of Scientific Intelligence (OSI) and the Office of Current Intelligence (OCI). Edward Tauss reported for the group that most UFO sightings could be easily explained, but recommended that the Agency continue monitoring the problem, in coordination with the Air Force Technical Intelligence Center (ATIC). He also urged that CIA conceal its interest from the media and the public, "in view of their probable alarmist tendencies".

Upon receiving the report, Deputy Director for Intelligence (DDI) Robert Amory, Jr. assigned responsibility for the UFO investigations to OSI's Physics and Electronics Division. Amory, who asked the group to focus on the national security implications of UFOs, was relaying concerns from the Director of Central Intelligence, Walter Bedell Smith. Smith wanted to know whether or not the Air Force investigation of flying saucers was sufficiently objective and how much more money and manpower would be necessary to determine the cause of the small percentage of unexplained flying saucers. Smith believed "there was only one chance in 10,000 that the phenomenon posed a threat to the security of the country, but even that chance could not be taken." According to Smith, it was the CIA's responsibility by statute to coordinate the intelligence effort required to solve the problem. Smith also wanted to know what use could be made of the UFO phenomenon in connection with US psychological warfare efforts.

After the Project Blue Book report, in 1967, the Air Force issued a contract to the University of Colorado for the study of UFOs. The principal investigator from the University was Dr. E.U. Condon, director of the National Bureau of Standards from 1946 to 1950. The project gained some support from the Central Intelligence Agency.[12] The 'Condon Report' was published in 1969.[13]

From the National Photo-Interpretation Center (NPIC), Condon's group was allowed access to classified material through the collateral[note 4] SECRET level (a relatively low level of intelligence category). Information was provided under the rules:[14]"

"Any work performed by NPIC to assist Dr. Condon in his investigation will not be identified as work accomplished by CIA. Dr. Condon was advised by Mr. Lundahl to make no reference to CIA in regard to this work effort. Dr. Condon stated that if he felt it necessary to obtain an official CIA comment he would make a separate distinct entry into CIA not related to contacts he has with NPIC.

"NPIC will not prepare any written comments, will not analyze information with the intent of drawing a conclusion, nor prepare written reports. NPIC personnel will be available to assist Dr. Condon by performing work of photogrammetric nature, such as attempting to measure objects imaged on photographs that may be part of Dr. Condon's analysis. Work performed by NPIC will be strictly of a technical nature using services and equipment generally not available elsewhere."

In summary, "At about 1235 the group adjourned to lunch and following lunch they left NPIC for a meeting with Brig. Gen Gillers at the Pentagon.

"Most all the discussion during the morning was of an unclassified nature dealing with primary fundamentals of photogrammetry, photographic analysis and problems related to the acquiring of enough information to conduct meaningful analyses."

Condon and the same group met again in May 1967 at NPIC to hear an analysis of UFO photographs taken at Zanesville, Ohio. The analysis debunked that sighting. The committee was again impressed with the technical work performed, and Condon remarked that for the first time a scientific analysis of a UFO would stand up to investigation.

Seriously, the list of crashed UFOs (complete with body counts!) reads like a history of general aviation fatalities. Yet we are told these are advanced beings with superior technology. If they are so advanced, why do they crash so readily? Conversely, if millions of visits to Earth have been made, their crash rate is a lot lower than, say, the United States' Interstate 25 highway.

As always, the evidence is "believed by some to be buried" or "reported recovered" or "the memo also states that it was believed" and even reports from foreign governments are somehow shut down by the US government. And every single scrap of wreckage is whisked away by the Air Force which is omnipotent in this area, but so incompetent they allowed B-52s to fly over the US, unaware they were carrying live nuclear weapons (for which the Secretary of the Air Force and Chief of Staff of the Air Force were sacked).

Unidentified Submerged Objects (USOs) are the lesser-known marine counterpart to UFOs. Like UFO reports, most USO sightings are either mundane, or impossible to verify. They are usually of the form "something glowing in the water", though the term sometimes is also used for the cases when a more traditional "flying saucer" decides to take a dive or rises from beneath the waves. *dramatic drums* If you have watched The Abyss or played X-COM: Terror from the Deep, you know what we are talking about.

In UFO books (and nowadays, websites) USOs are usually discussed together with ghost ships like the Mary Celeste, the Bermuda Triangle and mysterious collisions and accidents with submarines to reinforce the spooky mood and make you dread leaving the shore behind the horizon.

Note that bioluminescence is common in the ocean and there are a lot of glow-in-the-dark critters that rise to shallower waters during the night to feed. Note also that during the Cold War, ramming or getting rammed by a Soviet submarine could have far-reaching political consequences, so both parties tended to whistle innocently and pretend that nothing had happened. That didn't always work.

The Malibu Dome — roughly elliptical, with what look like supporting pillars. UFOlogists are convinced that it's an underwater base for extraterrestrials. Geologists call it the Sycamore Knoll, and identify it as an unusual feature caused by slumping in an earthquake zone. See This HuffPo article.

The Yonaguni Monument — A sophisticated alien base cleverly disguised as a pile of rocks.

“”It's a paradoxial state of affairs — the fact that ufologists are working so hard to "inform" (i.e. convince) the public of the existence of a phenomenon, the character of which ufologists themselves hardly care to investigate in any serious way.

How "unidentified" a phenomenon really is depends partly on the quality of the observation and the amount of effort invested in identifying it. Multiple observation locations and reasonably accurate bearings and azimuths can make identification much easier. Single observations of brief phenomena are more difficult to analyze.

There is a bit of a discrepancy between the evidence needed to show an extraterrestrial origin for UFOs and the evidence so far acquired and used by UFO enthusiasts. If they were real, it would — in principle — not be difficult to show their alien origin.

“”…despite the fact that we humans are great collectors of souvenirs, not one of these people has brought back so much as an extraterrestrial tool or artifact, which could, once and for all, resolve the UFO mystery.

—Philip Klass, on the lack of evidence

Now with the wide spread of cheap mobile phone cameras, high quality point & shoot cameras, as well as cheap, high definition handheld recorders an influx of much clearer and well-focused, UFO recordings are expected. Any time now. Aaaaaany time now… indeed, the quality of UFO evidence has not increased with the technological ability to capture it.

While we're at it, astronomerPhil Plait made an astute observation—assuming UFO sightings are of extraterrestrial origin, the group that should report them more than any other (at least per capita) would be amateur astronomers, since they watch the sky much more than other people... yet they actually make very few UFO reports. Plait suggests that this is precisely because they watch the sky more than other people, and much better understand what they see up there: they know not to be suspicious of routine phenomena (Jupiter and Venus are often reported as UFOs), and are likely to be able to identify unusual atmospheric phenomena—that is, they know what not to look for as being suspicious.

UFO proponents usually defend the lack of evidence based on a form of special pleading for UFOs. Perhaps science shouldn't discount eyewitnesses, no matter how drunk, or should drop some of its intellectual rigor for the sake of UFOs — say, to forget about reproducing any experiments, as most of the time no two UFO reports ever cite the same details with true independence.

While it can be assumed that a large proportion of UFO sightings are either mistakes or bullshit there are several examples of genuine weirdness surrounding UFOs. There have been numerous reports of UFOs by credible witnesses, ranging from airline pilots, to Mercury Astronaut Gordon Cooper, to former POTUSJimmy Carter. While these may have been, like other reports of UFOs, simple cases of mistaken identity, it proves that there are credible witnesses of UFO phenomena and that not everyone who sees them is batshit crazy. A notable example of odd behaviour by the government was the 2006 O'Hare International UFO sighting, during which over a dozen employees witnessed a flying disk over gate C-17. The FAA declined to investigate and stated the sighting was a "weather phenomenon." Many UFOlogists state that this runs counter to FAA regulation, which decrees that any potential security threat be investigated. Finally, during Project Blue Book, the last serious USAF investigation into the UFO phenomenon, the committee found that 701 reported cases remain unidentified. It must be noted that this does not mean alien, it means "unidentified."